During the past year the major focus of this project has been to study the mechanisms involved in the immune response to tumor antigens in experimental animals systems. Our approach has been multifaceted, employing numerous in vitro assays to gain insight into the immune reactions, and performing diverse in vivo experiments to determine which immune functions may play a role in tumor growth or regression. T-cell killing of tumor cells by lymphocytes has been studied in cytotoxicity assays Cr51 and IUdR125 release) using immune cells isolated from the tumor. Additional testing on the in vivo secondary response confirmed the in vivo role of the cytotoxic immune function. Studies on the specificity of the cytotoxic response have continued with emphasis on the possible role of H-2 antigens in syngeneic T-cell killing. Another T-cell dependent function, production of migration inhibition factor, has been extensively studied in order to expand our understanding of the tumor immune response. We have continued investigations into the role of the suppressor and growth inhibitory cells on the cellular and tumor immune response. Finally, we have continued work in the area of cryopreservation of immune function using normal and immune lymphoid populations and tumor cells for in vitro assays and for in vivo studies.